The Internet Protocol was originally developed with the assumption that users, each of which is assigned a unique Internet address, would be connected to the network at fixed locations. However, with the rapid acceptance of portable and handheld devices amongst consumers, the movement or migration of users about an individual network is typically the norm rather than the exception. The implicit design assumptions of the Internet Protocol are violated by this type of usage.
Radio access networks provide one of the most important network access technologies to extend the reach of the Internet to the mobile population, allowing mobile hosts to communicate with others at anytime, anywhere. Over the years, various mobility models have been proposed to support both wide-area macro-mobility and local-area micro-mobility, with an emphasis on primarily mobile-to-fixed and fixed-to-mobile network communication. These include for example Cellular IP, HAWAII, Mobile IPv4 and Mobile IPv6. These solutions, however, do not provide optimal routing paths for mobile-to-mobile communications because of the common requirement of routing IP packets through an anchor point in the network. However, as small and portable network devices rapidly penetrate the market, optimized mobile-to-mobile communication in metropolitan areas (e.g. Ottawa, Toronto) is crucial for the next generation of wireless Internet applications.
Typically, location information of a host is encoded in an Internet address (i.e. IP address). Therefore, in conventional systems, a mobile host must be located on the network at the location indicated by its IP address in order to receive IP packets. In such systems, a mobile host may need to change its IP address whenever it changes its point of access to the network for it to not lose its ability to communicate. Likewise, if a mobile host moves from one network to another, convention dictates that its IP address must also change.
Mobile IP attempts to deal with this issue, but suffers from triangular routing as a home agent is used as an anchor point. All downstream traffic for a mobile host always goes through the mobile's home agent. Mobile IP does not, therefore, guarantee an optimal routing path for mobile-to-mobile communications.
General Packet Radio Services (GPRS) provides data services in GSM networks. In GPRS, each mobile host is anchored with a GGSN and all packets from a mobile host always go through the same GGSN. As a result, the mobile-to-mobile routing path may not be optimal. GPRS uses GTP, a proprietary tunneling protocol between SGSN and GGSN. As a result, there is no provision for IP multicast in GPRS.
A solution is needed, therefore, whereby a mobile host does not lose any of its sessions due to a handoff. Specifically, some sort of mechanism is required to ensure that packets addressed to moving hosts can be successfully delivered with high probability.